<!DOCTYPE html>
<html>
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
	<title>值为false</title>
	<style type="text/css">
	* {
		padding: 0;
		margin: 0;
	}
    </style>
</head>
<body>
	<div class="container">
		<h1>值为false</h1>
	</div>

<script type="text/javascript">

var a, b = null
console.log(+a, Number(a));
console.log(+b, Number(b));

console.log(+null, Number(null), null == 0)
console.log(+undefined, Number(undefined), undefined == 0)
console.log(null > 0, null >= 0, null <= 0, null < 0, null == 0)
console.log('-----------------------\n')


console.log(''+ null, String(null));
console.log(''+ undefined, String(undefined));

</script>
</body>
</html>